The present invention relates generally to molecular electronics, and, more particularly, to vapor-sensitive, molecular light emitting diodes based on thin films of certain platinum complexes.
The inventors have recently published reports that have enucleated and explained the unusual xe2x80x9cvapochromicxe2x80x9d changes in absorption and emission spectra that result when certain stacked platinum complexes are exposed to organic vapors; see, e.g., C. L. Exstrom et al, Chemical Materials, Vol. 7, pp. 15-17 (1995) and C. A. Daws et al, Chemical Materials, Vol. 9, pp. 363-368 (1997).
A typical experiment involves a solution, crystal or solid film of material, such as tetrakis(p-decylphenylisocyano)platinum tetracyanoplatinate (I) (see FIG. 1, which depicts the chemical formula of the compound, where the dashed vertical line indicates the c-axis) that forms stacks of alternating cations and anions with strong inter-platinum interactions. These salts exhibit an intense absorption band in the visible region. Exposing the stacks to small molecule vapors, such as acetone or chloroform, leads to sorption of the vapor molecules in the free volume between the stacks, and produces shifts in the absorption and emission spectra. These xe2x80x9cvapochromicxe2x80x9d or xe2x80x9cvapoluminescentxe2x80x9d changes are usually reversible so that the original spectrum is regained quickly after the vapor is removed. Such an effect has potential application for sensor technology.
Molecular LEDs are under intense investigation; see, e.g., R. H. Friend in Conjugated Polymers and Related Materials, W. R. Salaneck et al, Eds., Chapter 21, Oxford University Press (1993); A. J. Heeger, in Conjugated Polymers and Related Materials, W. R. Salaneck et al, Eds., Chapter 4, Oxford University Press (1993); R. H. Friend et al, in xe2x80x9cPhysical Properties of Polymers Handbookxe2x80x9d, J. E. Mark, Ed., AIP Press, New York (1996); Y. Yang, MRS Bulletin, pp. 31-38 (June 1997); T. Tsutsui, MRS Bulletin, p. 39-45 (June 1997); and W. R. Salaneck et al, MRS Bulletin, p. 46-51 (June 1997). However, to the best of the inventors"" knowledge, there is only one unspecific report from the patent literature which describes this type of LED sensor; see, U.S. Pat. No. 5,629,533, issued to D. E. Ackley et al on May 13, 1997.
Vapochromic platinum complexes and salts have been the subject of a patent; see, U.S. Pat. No. 5,766,952, issued to Kent R. Maim et al on Jun. 16, 1998. Such complexes change color when exposed to certain organic vapors.
In accordance with the present invention, a molecular light emitting diode is provided. The molecular LED employs an organic complex that acts as both a sensor to certain organic molecules, or analyte vapors, and as an active light emitter. The molecular LED of the present invention comprises:
(a) a first electrode;
(b) a hole transport layer formed on the first electrode;
(c) a sensing/emitting layer formed on the hole transport layer, the sensing layer comprising a material that changes color upon exposure to the analyte vapors;
(d) an electron conductor layer formed on the sensing layer; and
(e) a second electrode formed on the electron conductor layer,
wherein the hole transport layer emits light at a shorter wavelength than the sensing/emitting layer and wherein at least the first electrode comprises an optically transparent material. The device is preferably formed on a transparent dielectric substrate, on which the first electrode is formed.
Also in accordance with the present invention, a method is provided for detecting analyte vapors. The method comprises:
(a) providing the above-described vapochromic LED;
(b) introducing the analyte vapors to the sensing layer; and
(c) biasing the first electrode positive with respect to the second electrode.
Further in accordance with the present invention, methods are provided for forming the vapochromic LED.
Other objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed description and accompanying drawings, in which like reference designations represent like features throughout the FIGURES. The drawings referred to in this description should be understood as not being drawn to scale except if specifically noted.